In an internal combustion engine having a fuel injection system, it is necessary to inject the correct amount of fuel into the engine to produce a stoichiometric fuel/air mixture to produce satisfactory operation of the engine. In stationary conditions this is the state of the art. However, as the load on the engine increases, the amount of air drawn into each cylinder increases accordingly, and it is necessary to increase the amount of fuel injected. Conversely, as the load on the engine decreases it is necessary to reduce the amount of fuel injected. The correct matching of the air/fuel ratio even in these dynamic conditions is still a problem.
In present systems it is usual to provide a sensor in the air inlet system of the engine to give a measure of the engine load in the form of an electrical signal as a basis for calculating the amount of fuel which needs to be injected. Examples of such sensors are a pressure sensor, a hot film or hot wire air mass meter and a flap-type meter. The signals obtained from such sensors follow the load very accurately during constant load conditions and even during slowly-changing load conditions. However, under rapidly-changing load conditions, the signals obtained are inaccurate and lead to mismatching of the injected fuel. For example, the signals evaluated from a pressure sensor can only follow the true change in the load slowly with a certain delay, and thus signals obtained from it for the amount of fuel calculated therefrom to be injected produces a lean mixture. Signals from the other types of sensors mentioned overshoot considerably the value corresponding to the true load during rapidly-changing load conditions due to the fact that they measure the air drawn into the manifold which must first be filled with air, before the actual cylinder charge is increased. In some cases, after a first overshoot of the signal an undershoot occurs, especially in the case of a flap-type meter. The result is a fuel/air mixture which can excessively be rich or lean. A further reason for mismatching of the air/fuel ratio during load changes is the resulting variation of the fuel wall film which needs to be compensated for by special algorithms.
It is an object of the present invention to provide a fuel injection system for an internal combustion engine which is able to follow a rapidly-changing load more closely, and to maintain the desired air/fuel ratio.